Understanding the genetic regulation of acidity in Citrus fruit

Atkins, Elliott (2022) Understanding the genetic regulation of acidity in Citrus fruit. Doctoral thesis, University of East Anglia.

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Citrus is the most economically important genus in the family Rutaceae. Fruit acidity is also a major determinant of fruit and juice taste, but its regulation has not been elucidated. Improvements through breeding, while difficult, could be better informed by understanding the genetic regulation of fruit acidity in Citrus at the molecular level. In this study, I used RNA sequencing transcriptomic data, phylogenetic analyses, and metabolic characterisation of acidless C. sinensis varieties to propose a model for the regulation of hyperacidification in Citrus fruits. By analogy the mechanism in Petunia, the AtMYB5 and PhPH4 homolog Nicole forms a complex with bHLH transcription factor Noemi, to govern fruit acidity and citrate accumulation via transcriptional regulation of PH-like genes.

Phylogenetic analyses of the C. sinensis genome and genotypic analyses of acidless varieties Sorocaba, Verde R1 and Verde R2 led to the discovery of nicolesoro, a mutant allele of Nicole containing an LTR-retrotransposon insertion which has disrupted functionality. These varieties provide the first example of disassociation of the pleotropic link between acidity and proanthocyanidin (PA) biosynthesis in an acidless Citrus mutant. Nicole is not essential for PA biosynthesis in Citrus due to the accumulation of PAs in mutant seeds, and uniquely has lost the ability to activate the expression of PA transporter CsTT12, typically activated by AtMYB5 homologs. Conversely, Nicole can directly activate P3A- and P3B-ATPases, CsPH5 and CsPH1, to facilitate hyperacidification and citrate accumulation by avoiding the counteraction of H+/PA-antiporter, CsTT12.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Nicola Veasy
Date Deposited: 23 Mar 2023 09:55
Last Modified: 23 Mar 2023 09:55
URI: https://ueaeprints.uea.ac.uk/id/eprint/91657


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